Building and maintaining solar and wind power projects can be hazardous, and industry watchdogs worry that the push for more green energy places more workers and bystanders in harm's way.

They can look benign from a distance — solar panels glistening in the sun or turbines gently churning with the breeze to produce electricity for hundreds of thousands of homes. But building and maintaining them can be hazardous.

Accidents involving wind turbines alone have tripled in the last decade, and watchdog groups fear incidents could skyrocket further — placing more workers and even bystanders in harm's way — because a surge in projects requires hiring hordes of new and often inexperienced workers.

Last year, the solar industry grew 67% and doubled its employment in the U.S. to 100,000 workers, according to the Solar Energy Industries Assn. The wind industry supports more than 75,000 jobs.

The concerns have a particular resonance in California, home to many of the nation's largest solar and wind projects.

"We're hearing about more and more incidents," said Lisa Linowes, executive director of watchdog organization Industrial Wind Action Group. "One of these days, a turbine's going to fall on someone."

Many wind turbine technicians work in a bathroom-size space 20 stories above ground surrounded by high-voltage electrical equipment. Some inspect turbine blades while suspended alongside them, on sites whipped by strong winds. Components can weigh more than 90 tons.

Technicians have fallen hundreds of feet; others have been crushed by wayward parts or trapped in twisting machinery. Pilots in small planes have crashed into the towers. Electrical explosions last year left a worker in Illinois with third-degree burns and two others in San Diego County with similar injuries.

Workers could asphyxiate inside turbine enclosures or inhale harmful gases and vapors when buffing and resurfacing blades, the Department of Labor cautions.

Wind turbine accidents involving injuries and equipment damage have surged over the last decade, peaking in 2008 with 128 incidents worldwide, according to the Caithness Windfarm Information Forum. Since the 1970s, there have been 78 fatalities, with about half in the U.S.

The number of solar incidents is harder to gauge, but most industry workers say it's rising. Solar workers perform tasks similar to those in the most dangerous professions: roofing, electrical work and carpentry.

In April 2010, Hans Petersen was taking a break from graduate theology studies and had been installing solar panels for six months when he stumbled off the sloped roof at a Northern California public housing complex and plunged 45 feet to his death.

Petersen, 30, wasn't wearing a safety harness. The gear, which could have prevented the fall, wasn't an industrywide requirement at the time.

"They just took some things for granted — that this roof was not a particularly dangerous roof, that the pitch was modest," said Petersen's father, the Rev. Glenn Petersen. "I'm sure Hans didn't expect anything. He felt comfortable" at those heights.

Even the public can be at risk, watchdog groups say. Fires atop wind towers have scattered burning debris, according to neighbors, who also describe hastily built wind installations collapsing within months and harsh weather conditions exacerbating wear and tear.

The complicated wiring under solar panels has left some firefighters so bewildered that they have allowed residential rooftops to burn. Some panels contain materials such as cadmium and selenium, which could be explosive or even carcinogenic, according to the Silicon Valley Toxics Coalition.

Panel parts can also be flammable or prone to melting, or torn off in storms or cracked by hail, testing experts said.

With production costs shrinking, companies are under "tremendous pressure" to stay competitive, "sometimes using less durable components," said Jeffrey Smidt, general manager of the Global Energy Business at product certification company Underwriters Laboratories Inc., commonly known as UL.

"People just assume they're fine," he said.

Watchdog groups say a hodgepodge of state and federal renewable energy safety standards haven't kept up with the growth of the industry. Some were adapted from other industries and don't specifically cover wind and solar projects, while others are guidelines rather than mandatory regulations. Many are old and are just now being updated.

But clean-energy companies say they are backing more uniform safety standards and offering intensive training for workers.

This year, the American Wind Energy Assn. launched a program to collect safety data for the industry. It also has online advisories that include warnings about working in high winds, requirements for fall protection above six feet and recommendations for frequent crane inspections and lightning safety plans.

The solar industry trade group said it is working on its own set of best practices. The organization has offered safety recommendations for an international construction standard being drafted for renewable energy projects.